Upgrades selenium-webdriver to use latest

  - fixes an issue with latest firefox on osx, where first test would fail due to an erroneous timeout
  - capybara 2 is more finnicky when it comes to ambiguous matches (it doesn't allow for them)
  - fixed a remote link to use POST for a test that should have been failing with previous capybara, since there's no route for `GET /rsvp`